Thesis deals about solution of non-steady flow in hydraulic systems, which have one dominant component of velocity. Such systems can be arbitrarily structured and they are not limited by number of elements. Computation is based on Lax-Wendroff method and enables considering of variable sound peed as function of static pressure and properties of pipe material. It means, that hydraulic system can be very various. Numerical method is described in detail and description is also focused on sensitivity of method for time step and length step. It can be very imported for evaluation of numerical viscosity, which is compared with second viscosity of fluid. Hammer is working title of software, which was developed on the basis of written numerical procedures. This software enables fast computation of flow in pipe-line systems.

<p>With their advantages of low-cost, high-reliability and simplicity, external gear pumps (EGPs) are popular choices in many applications, such as mobile hydraulic control system, fuel injection, and liquid transportation system, to name a few. Like other positive displacement machines, EGPs are characterized by a flow non-uniformity, which is given by the gear meshing and results in vibrations and noises. With increasing demands for low-noise components required by modern fluid-power systems, new designs of external gear machines with less noise emission and lower pulsation production are highly desired by the industry. </p><p><br></p><p>To satisfy these demands, there are several new-generation gear pump designs that have been realized by the industry and already commercialized. However, the research from both academia on external gear pumps are still primarily focused traditional involute gear pumps, while state-of-the-art research on these new-generation external gear pumps are highly lacked. Also for the most novel designs recently released to the market, their designs still have large margin to improve, as some of the physics inside these gear machines are not well understood and formulated. The goal of this research is to fill in this gap, by gain understanding of the relations between design features and actual flow generated by such novel designs, and provide general methods of analysis and design for efficient and silent units. </p><p><br></p><p>To achieve this goal, this PhD dissertation presents a comprehensive approach of analysis for external gear pumps, with the emphasis on the new-generation helical gear pumps. The discussion covers a large variety of aspects for gear pump design and analysis, including: the analysis on the gear profile design and meshing, the displacement-chamber geometric modeling, and the kinematic-flow analysis. They are followed by a dynamic simulation model covering the dynamics of fluids, forces, and micro-motions, together with simulation results that provides the insights into the physics of new-generation gear machines. Multiple experimental results are provided, which show the validity of the simulation models by matching the pressure ripple measurement and the volumetric efficiencies. Furthermore, a linearized analysis on the ripple source of gear pumps are described, in order to provide the connection and understanding of the pump-generated ripple to the higher-level system analysis, which is also missing from the past academia research. In addition, the some of the models are utilized in optimization studies. These optimization results show the potentials of using the proposed approach of analysis to improve the existing designs as well as development of more efficient and silent units.</p><div><br></div>

Condition monitoring of hydraulic systems has become more available and inexpensive to implement. However, much of the research on this topic has been done on stationary hydraulic systems without the jump to mobile machines. This lack of research on condition monitoring of hydraulic systems on mobile equipment is addressed in this work. The objective of this work is to develop a novel process of implementing an affordable condition monitoring system for axial piston pumps on a mobile machine, a mini excavator in this work. The intent was to find a minimum number of sensors required to accurately predict a faulty pump. First, an expert understanding of the different components on an axial piston pump and how those components interact with one another was discussed. The valve plate was selected as a case study for condition monitoring because valve plates are a critical component that are known for a high percentage of failures in axial piston pumps. Several valve plates with various degrees of natural wear and artificially generated damage were obtained, and an optical profilometer was used to quantify the level of wear and damage. A stationary test-rig was developed to determine if the faulty pumps could be detected under a controlled environment, to test several different machine learning algorithms, and to perform a sensor reduction to find the minimum number of required sensors necessary to detect the faulty pumps. The results from this investigation showed that only the pump outlet pressure, drain pressure, speed, and displacement are sufficient to detect the faulty pump conditions, and the K-Nearest Neighbor (KNN) machine learning algorithms proved to be the least computationally expensive and most accurate algorithms that were investigated. Fault detectability accuracies of 100% were achievable. Next, instrumentation of a mini excavator was shown to begin the next phase of the research, which is to implement a similar process that was done on the stationary test-rig but on a mobile machine. Three duty cycle were developed for the excavator: controlled, digging, and different operator. The controlled duty cycle eliminated the need of an operator and the variability inherent in mobile machines. The digging cycle was a realistic cycle where an operator dug into a lose pile of soil. The different operator cycle is the same as the digging cycle but with another operator. The sensors found to be the most useful were the same as those determined on the stationary test-rig, and the best algorithm was the Fine KNN for both the controlled and digging cycles. The controlled cycle could see fault detectability accuracies of 100%, while the digging cycle only saw accuracies of 93.6%. Finally, a cross-compatibility between a model trained under one cycle and using data from another cycle as an input into the model. This study showed that a model trained under the controlled duty cycle does not give reliable and accurate fault detectability for data run in a digging cycle, below 60% accuracies. This work concluded by recommending a diagnostic function for mobile machines to perform a preprogrammed operation to reliably and accurately detect pump faults.

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The automation of hydraulic mobile machinery, such as excavators, requires high performance control solutions. In hydraulics, this means fast and accurate force, velocity and position control of hydraulic cylinder. Especially the force control is known to be difficult with traditional servo valves. Fast digital hydraulic valves together with modern control solutions can overcome this problem. This paper uses a new force control solution, which is based on the fast digital hydraulic valves and model based control principle. The control solution is applied in a heavy axis mimicking dynamics of mobile machine booms. Experimental results show good force, velocity and position tracking performance with varying load masses. The slow velocity performance is also much improved when compared to the earlier results.

Speed and displacement variable pumps offer a degree of freedom for process control. As a certain operation point can be supplied by different combinations of drive speed and pump displacement intelligent control strategies can address major issues like energy efficiency, process dynamics and noise level in industrial applications. This paper will provide an overview of recent research and development activities to evaluate the named potentials.

During the past three years the Institute for Fluid Power Drives and Controls in Aachen has developed a new hydraulic system for mobile machinery called STEAM. The system represents a new step in excavator hydraulics, as it aims to reduce both the hydraulic system losses as well as those of the internal combustion engine by using a hybrid hydraulic architecture with accumulators. Starting with initial simulation studies the development has been followed by scaled test bench measurements and has progressed to a full scale validation using an 18 t excavator. The following publication aims to summarise the results obtained thus far with the aim of making them available to industry and encouraging their implementation in future applications.

Liebherr mobile harbor cranes use electrical generators to provide electrical power for load attachment devices such as container spreaders or magnets. Upcoming exhaust and noise emission standards and energy saving considerations lead to a broad diesel engine speed range. The challenging design aspect is to ensure a constant speed of the asynchronous generator by the hydraulic drive system. In addition, electrical load profiles of inductive consumers usually have DT1 system characteristics with very small time constants. They evoke fast torque variations interfacing the hydraulic transmission. Liebherr mobile harbor cranes, see Figure 1, usually have a closed hydraulic circuit containing a hydraulic pump with a high displacement volume that is adjusted electronically in accordance to the current diesel engine speed. Regarding the energy saving aspects, a further minimization of the diesel engine speed leads to a larger pump size with increasing torque losses. Depending on the pressure setting, the volume flows can be reduced in constant pressure grids. Especially in part-load operation this results in better efficiency compared to closed hydraulic circuits by minimizing the displacement volume of hydraulic components. To obtain a stable generator speed, it is essential to adjust the displacement volume of the hydraulic unit for equalizing its input torque with the Figure 1: LHM 800 Group 10 - Mobile Hydraulics | Paper 10-5 199 generator load torque. In interaction with the software-based control architecture, the stability of the electrical frequency depends on the mass inertia of the generator drive and time constants of the embedded hydraulic actuators. The system model, represented by ODEs is established and verified with a hydraulic simulation software. On that basis, the design approach of a PI-state-controller is presented. Corresponding controller gains and state feedback parameters are determined by pole placement techniques. To conclude this investigation a comparison between the hydraulically closed circuit and the constant pressure grid is shown by simulation and measurement data.

<div><p>Water is inflammable, non-toxic, environmentally friendly--- desirable traits, for a hydraulic fluid. However, its extremely low viscosity diminishes the load-bearing and sealing capacity of lubricating interfaces. Case in point: axial piston machines of swash plate design are compact, highly efficient positive displacement machines at the heart of hydraulic systems in forestry, construction, aerospace, and agricultural equipment, as well as industrial applications (presses, etc.); however, the three main lubricating interfaces decisive to the performance of such units in terms of both component life and efficiency are challenged by the use of water as working fluid. Especially during high-pressure operation, this low-viscosity lubricant can cause the these interfaces to fail in carrying the imposed load, resulting in severe wear, or even pump failure. The piston-cylinder interface is particularly challenging to design for water because it stands under obligation to carry the heavy side load that acts on the pistons of these machines, which increases with operating pressure. Furthermore, the architecture of axial piston machines of swash plate design does not allow this interface to be hydrostatically balanced.</p> <p> </p> <p>Through the development of a methodology that separates the fluid pressure fields of the three main lubricating interfaces of axial piston machines into their hydrostatic and hydrodynamic components, the present work enables a direct comparison of these interfaces in terms of how they support load. A case study of a 75 cc unit running on hydraulic oil conducted via this methodology at three different operating conditions (low pressure/low speed, low pressure/high speed, and high pressure/low speed) demonstrates that in the piston-cylinder interface, the force from hydrostatic pressure reaches such high magnitudes over the high-pressure stroke that less than half of it is needed to counter the load. The excess force from hydrostatic pressure then becomes the load. Consequentially, hydrodynamic pressure must counter a force from hydrostatic pressure that exceeds the original load. In the other two interfaces, by contrast, over half the load is being carried by hydrostatic pressure, thus significantly diminishing the amount of hydrodynamic pressure the interfaces are required to generate in order to achieve full load support. Moreover, nearly all of the moment on the piston is countered by hydrodynamic pressure, while less than half of the moment on the block is countered by hydrodynamic pressure, and the moment on the slipper is negligible by comparison.</p> <p> </p> <p>While this case study only investigates one pump, it shows how critical hydrodynamic pressure can be to load support in the piston-cylinder interface. The use of a low-viscosity fluid, e.g. water, reduces the hydrodynamic pressure that is generated in this interface, which, at challenging operating conditions, can lead to metal-to-metal contact. However, the performance of the interface can be improved via micro surface shaping, i.e. by giving the surface of the piston, or the bore that it moves through, a shape on the order of microns in height. The aim of present work is to pursue design trends leading to surface shapes that will enable this interface to function at higher pressures than currently achievable. </p> <p> </p> <p>This pursuit takes the form of systematic virtual design studies, an optimization procedure, and an algorithm developed specifically for tailoring the bore surfaces through which the pistons travel to piston tilt and deformation. From this emerges not only a set of design trends corresponding to the dimensions of two particularly powerful types of micro surface shaping, but also a profound insight into the behavior of the water-lubricated piston-cylinder interface fluid film, and how that behavior can be manipulated by changing the component surfaces that constitute its borders. Furthermore, in collaboration with Danfoss High Pressure Pumps, a physical prototype of a 444 cc axial piston pump with surface shaping generated via the aforementioned algorithm has been constructed and tested, achieving a total pump efficiency roughly 3% higher than that achievable by the commercial unit that the geometry of the prototype is based on.</p><br></div>

Komatsu Forest AB in Umeå saw an opportunity to increase performance during fast varying loads, e.g., when starting to feed after the felling cut, that proved more difficult to reach with their new line of stage V forest harvesters. It was believed that this issue was magnified as a result of new environmental regulations which limited their diesel engines' fuel injection quantity with low turbo boost pressure. It was in Komatsu Forest's interest to make comprehensive measurements of hydraulic and engine parameters in order to investigate what was limiting performance. This thesis includes a literature study into a number of viable options for storage types for a heavy hybrid vehicle with the purpose to recommend the best suited type for Komatsu's harvesters. It also includes extensive measurements made on a producing harvester where hydraulic and engine parameters as well as for example valve currents were logged and used as grounds in making the energy storage recommendation. With results from the measurements, the goal was to estimate how much energy is needed, how much energy can be stored and lastly to design an energy storage to supply additional power to increase performance. With successful measurements, it was possible to detect that approximately five kJ of energy with a maximum momentary power of 37 kW was sufficient to achieve a smoother first feeding. Furthermore, approximately 9-14 kJ of energy and between 0,3 and 0,5 l of hydraulic fluid was estimated as potential stored energy and volume from feeding stops of different sized trees plus an additional 3 kJ and 0,1 l of fluid from cutting stops. The best suited energy storage then proved to be an accumulator mounted on the P-line, which resulted in an appropriate accumulator volume of 4 l with an estimated pressure range of 250-280 bar.